System and a method for detecting wear of a ball-joint connection device of a rod, a rotor assembly, and an aircraft

ABSTRACT

The present invention relates to a detection system for detecting wear of a ball-joint connection device of a pitch rod. The detection system includes at least one measurement assembly, said at least one measurement assembly having at least one deformation gauge for placing on said pitch rod, said detection system comprising at least one electrical conditioning circuit connected to at least one said deformation gauge and to at least one electrical energy source, said electrical conditioning circuit being configured to generate a measurement signal that varies as a function of deformation of said at least one deformation gauge and as a function of said wear.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of FR 19 01377 filed on Feb. 12,2019, the disclosure of which is incorporated in its entirety byreference herein.

FIELD OF THE INVENTION

The present invention relates to a system and to a method for detectingwear of a ball-joint connection device of a connecting rod, to a rotorassembly, and to an aircraft provided with such system.

BACKGROUND OF THE INVENTION

In order to make a ball-joint connection between two mechanical parts,an operator can make use of a ball-joint connection device. Such adevice is sometimes referred to more simply as a “ball-joint”.

A ball-joint connection device may comprise an outer cage and a ball.The ball is then inserted in the outer cage in order to be rotatablymovable relative to the outer cage. Anti-fiction means may be interposedbetween the spherical ball and the outer cage. The anti-fiction meansmay be fastened to the inner wall of the outer cage so as to face thespherical ball, or conversely they may be fastened to the outer wall ofthe spherical ball so as to face the outer cage. Such anti-fiction meansmay be referred to as a “liner”.

The ball itself is sometimes referred to as a “ball-joint” or indeed asan “inner ring”, for example. The ball is sometimes also referred to asa “spherical ball”. Nevertheless, such terminology can appearinappropriate insofar as the ball sometimes includes at least one flator even two flats at two diametrically opposite ends. Thus, the ball isin fact a sphere that is truncated at at least one pole. A ball may alsobe secured to a rod or it may have a rod passing through it. The term“ball” is used below.

Under such conditions, the outer cage may be fastened by conventionalmeans to a first mechanical part. Likewise, the ball may be fastened toa second mechanical part, e.g. by using a fastener rod passing rightthrough the ball via its truncated poles.

Such ball-joint connection devices are in widespread use. In particular,a rotor of an aircraft, e.g. such as a main rotor of a helicopter, mayinclude pitch rods for controlling the pitch of its blades. By way ofexample, a pitch rod is hinged firstly to a rotary swashplate of a setof swashplates by means of a first ball-joint device, and secondly to apitch lever by means of a second ball-joint device. The outer cage ofeach ball-joint device is then secured to a member of the rod, the ballof the first ball-joint device being secured to the rotary swashplate ofthe set of swashplates, and the ball of the second ball-joint devicebeing secured to the pitch lever.

Ball-joint devices are effective. Nevertheless, the anti-fiction means,and/or the ball, and/or the outer cage naturally erode during thelifetime of the ball-joint connection device. The resulting wear leadsto unwanted clearance being created between the ball and the outer cage.On an aircraft rotor pitch rod, such play has a harmful impact on thecontrol of the aircraft. Consequently, this wear ends up with theball-joint connection device being replaced as a function of a removalcriterion determined by the manufacturer. The removal criterion mayconsist in a maximum amount of clearance that is acceptable between theouter cage and the ball.

Nevertheless, such clearance is difficult to measure and measurement mayneed to be performed following a procedure that can be lengthy andrelatively expensive. For example, the procedure may require each pitchrod to be dismantled by performing the following actions: an operatorgetting up to the level of the rotor by using a ladder or a platform,opening a protective cover, preparing the rotor, e.g. by setting a bladepitch and/or by preventing the rotor from rotating, dismantling therods, verifying the clearance of each rod, reassembling the rods,releasing the rotor, closing the protective cover, and the operatorgetting back down.

In addition to the relatively long duration of that procedure, anoperator needs to make use of various tools in order to perform thatmaintenance action, which can make it more complicated to carry out.Also, that procedure implies that the clearance is evaluated by a humanbeing, which evaluation might therefore be erroneous.

Documents US 2008/036617, FR 2 599 793, WO 2014/153518, and WO2018/152277 are also known.

SUMMARY OF THE INVENTION

An object of the present invention is thus to provide a system thatfacilitates detecting a ball-joint connection device that is worn to adegree that requires the ball-joint connection device to be removed.

The invention provides a detection system for detecting wear of aball-joint connection device of a pitch rod of a rotor assembly.

The detection system includes at least one measurement assembly, the atleast one measurement assembly having at least one deformation gauge forplacing on a pitch rod that is to be monitored, the detection systemcomprising at least one electrical conditioning circuit connected to atleast one said deformation gauge and to at least one electrical energysource, the electrical conditioning circuit being configured to generatea measurement signal that varies as a function of deformation of said atleast one deformation gauge and as a function of said wear.

The system may include one or more electrical conditioning circuits foreach measurement assembly, possibly arranged on one or more electronicscards. Likewise, the system may comprise one or more electrical energysources for each measurement assembly, it being possible for a singleelectrical energy source to power one or more electrical conditioningcircuits. For example, each measurement assembly may comprise aplurality of subassemblies, each provided with at least one deformationgauge, the system comprising an electrical conditioning circuit for eachsubassembly and an electrical energy source for each electricalconditioning circuit.

Furthermore, and by way of example, the electrical conditioning circuitmay comprise a conventional Wheatstone bridge circuit. The electricalconditioning circuit includes a member that generates the measurementsignal, e.g. such as a member measuring a difference of electricpotential or of electric current, or indeed a capacitance. An electricalconditioning circuit may include an output for transmitting themeasurement signal to another member for processing and/or may include amemory for storing each measurement signal in order to be able to use itsubsequently. An energy source may comprise at least oneoptionally-rechargeable battery, at least one electrical energyharvesting system . . . .

Such a detection system can serve to evaluate the presence ofunacceptable clearance in a ball-joint connection device of a rod, andin particular of a pitch rod of an aircraft rotor, and for exampleclearance that is small and greater than or equal to 0.25 millimeters(mm).

In operation, the commands applied by a human pilot or by an autopilottogether with the movements of the blade connected to the pitch rodeither directly or via a cuff, for example, and the vibration of therotor all generate forces exerted on the pitch rod. Those forces deformthe pitch rod. However, a pitch rod deforms differently in the presenceof unacceptable clearance in one of its ball-joint connection devices.Surprisingly, predetermined indicators applied to the raw or processedmeasurement signal can enable such clearance to be identified.

Under such circumstances, the detection system is provided with at leastone deformation gauge, e.g. an axial traction or bending strain gauge,arranged on a pitch rod in order to act in conventional manner tomeasure deformation of the pitch rod in real time. The measurementsignal generated by the electrical conditioning circuit from thedeformation of the deformation gauge, which is an image of thedeformation of the pitch rod, is then used to identify the presence ofclearance to a degree that requires a maintenance action. Themeasurement signal may be used to obtain one or more indicators in thetime domain or in the frequency domain, and to determine whethermaintenance action needs to be undertaken by studying these indicators.The measurement signal may be used in real time, or subsequently. Themeasurement signal may be used on board the aircraft or externallytherefrom.

Specifically, for a given pitch rod, the measurement signal varies as afunction of the wear of the ball-joint connection device, with thisvariation being detectable in the presence of unacceptable clearance byperforming particular analysis in the time domain and/or in thefrequency domain.

Consequently, the present invention proposes monitoring the wear of aball-joint connection device by using at least one deformation gaugecarried by a pitch rod and by analyzing the measurement signal, e.g. bycomparing it with a stored threshold that has been determined bytesting. This procedure therefore does not require a pitch rod to bedismantled in order to be tested.

Furthermore, the detection system can provide safety insofar asexcessive wear is detected automatically at least in part by thedetection system, thereby making it possible to reduce the risk of aworn pitch rod being left in place as a result of human error inassessing wear.

Under such circumstances, the detection system may be arranged at leastin part on a rotor in order to detect when clearance in a ball-jointconnection of a pitch rod becomes excessive without any need fordismantling, nor even any need to require an operator to get up on therotor. The detection system acts in innovative manner to detect unusualdeformation of the pitch rod during a flight and to report on the stateof the ball-joint connections.

The detection system may also include one or more of the followingcharacteristics.

In one aspect, the detection system may comprise monitoring calculationmeans in communication with said at least one electrical conditioningcircuit, the monitoring calculation means being configured to processsaid measurement signal and to determine the presence of said wear to adegree that requires maintenance action on said pitch rod when saidmeasurement signal as processed by the monitoring calculation meanspresents a predetermined anomaly.

Such an anomaly may be in the form of a time-varying measurement signalexceeding a stored threshold, or in the form of a frequency component ofa signal in the frequency domain having an amplitude that is greaterthan or less than a stored threshold. Such a frequency component of asignal in the frequency domain may be in the form of a line in aspectral plot.

A single measurement assembly may have its own dedicated monitoringcalculation means, or the monitoring calculation means may be sharedamong a plurality of measurement assemblies.

Each measurement assembly of the detection system may include one ormore monitoring calculation means, possibly arranged on one or moreelectronics cards. For example, each measurement assembly may comprise aplurality of subassemblies, each provided with at least one deformationgauge, the detection system comprising an electrical conditioningcircuit for each subassembly and indeed an electrical energy source foreach electrical conditioning circuit. Alternatively, single monitoringcalculation means may be dedicated to a plurality of subassemblies.

Furthermore, the monitoring calculation means may be arranged in arotary reference frame of an aircraft by being carried by a pitch rod orby a rotary member of a rotor assembly. The monitoring calculation meansmay also be offset in a non-rotary reference frame, being connected bywired or wireless connections to at least one electrical conditioningcircuit. Alternatively, or in addition, the monitoring calculation meansmay be offset away from the aircraft, being configured to be connectedby wired or wireless connections to at least one electrical conditioningcircuit.

Independently of the way in which the monitoring calculation means arearranged, the monitoring calculation means communicate with at least oneelectrical conditioning circuit in order at least to recover one or moremeasurement signals so as to determine the presence of a predeterminedanomaly in order to estimate whether a ball-joint connection devicepresents unacceptable clearance. The monitoring calculation means mayinclude a memory storing at least one measurement signal prior toprocessing and/or at least one measurement signal after processingand/or information indicating whether a ball-joint connection is worn,such as for example a determined value for the clearance or a Booleanvalue representative of a healthy or worn state. For example, while onthe ground, a ground maintenance operator may recover one or moremeasurement signals stored in at least one monitoring calculation meansvia a wireless connection with such monitoring calculation means, andthen process that signal. In another example, while on the ground, aground maintenance operator may recover information stored in on-boardmonitoring calculation means and indicating directly whether aball-joint connection device is worn.

In one aspect, the detection system may include warning means incommunication with said monitoring calculation means, the monitoringcalculation means being configured to control the warning means in orderto signal the presence of wear when said measurement signal as processedpresents said predetermined anomaly.

Optionally, monitoring calculation means may process each measurementsignal by applying a robust algorithm in order to estimate whether theball-joint connection device presents wear to a degree that requires amaintenance action. If so, the calculation means may operate warningmeans to indicate in tactile, visual, or audible manner that the pitchrod needs to be subjected to a maintenance action, e.g. within apredetermined time period. Such warning means may be in the form of atactile, visual, audible, . . . system. By way of example, a housing maycontain monitoring calculation means together with a light-emittingdiode (LED) of the warning means, with the monitoring calculation meansswitching on the LED if unacceptable clearance is detected whileprocessing a measurement signal.

In one aspect, said detection system may include at least a firstantenna for transmitting away from the rotor assembly either themeasurement signal or else a signal emitted by the monitoringcalculation means connected to an electrical conditioning circuit, saidfirst antenna being connected to the electrical conditioning circuit orto the monitoring calculation means.

Optionally, the monitoring calculation means may be shared between aplurality of measurement assemblies and may be connected to a firstantenna.

Optionally, an electrical conditioning circuit may be connected to afirst antenna that communicates with a second antenna of the monitoringcalculation means.

In one possibility, each measurement assembly may be fastened directlyto the pitch rod that is to be monitored. Likewise, an electricalconditioning circuit and/or an electrical energy source and/oroptionally monitoring calculation means and/or a first antenna may befastened directly to the pitch rod in order to avoid wiring constraintsin a rotary reference frame. In one possibility, each pitch rod maypresent its own detection system.

Under such circumstances, the detection system may include attachmentmeans for fastening at least one measurement assembly directly on apitch rod. Likewise, attachment means may be used for fastening anelectrical conditioning circuit, and/or an electrical energy source,and/or optionally monitoring calculation means, and/or a first antennadirectly on a pitch rod.

For example, the attachment means may comprise adhesive or theequivalent, welding, a screw fastener system, an attachment collar,these examples being given by way of example.

In one aspect, said detection system may include a carrier, said carrierbeing provided with a fastener device for fastening to the pitch rodthat is to be monitored, said carrier including an elasticallydeformable measurement segment carrying a said measurement assembly.

The term “faster device for fastening to the pitch rod that is to bemonitored” covers one or more elements contributing to holding thecarrier on a pitch rod, e.g. to members suitable for clamping betweentwo nuts of the pitch rod.

This variant can avoid any need to modify a pitch rod physically inorder to install a measurement assembly thereon. A carrier may bearranged on a pitch rod in a manner that is reversible andnondestructive. At least one deformation gauge may be fastened to thecarrier, with the carrier constituting a housing carried by the pitchrod, for example. By way of example, each pitch rod of a rotor assemblymay be fitted with such a carrier.

Optionally, the carrier and the members carried by the carrier may forma piece of equipment that presents a center of gravity that ispositioned substantially on a central axis of the carrier, the centralaxis coinciding with the longitudinal extension direction of a pitch rodwhen the carrier is carried by the pitch rod. Thus, the carrier isbalanced so as to avoid giving rise to additional stresses in the pitchrod in order to avoid degrading the measurements and in order to avoidthe piece of equipment turning about the pitch rod. This variant canpotentially avoid giving rise to new modes of wear, e.g. by not causinga rod to turn about its own longitudinal axis.

In one aspect, the measurement segment may include at least one saidenergy source and/or at least one said electrical conditioning circuit.For example, at least one energy source and/or at least one electricalconditioning circuit may be embedded in the measurement segment or maybe fastened to a wall of the measurement segment.

In one aspect, the carrier may present a first segment including atleast one said electrical energy source, said carrier presenting asecond segment including at least one electrical conditioning circuit.

The first and second segments may be distinct, or they may coincide.

Optionally, the carrier may also carry other members of the detectionsystem in order to form a piece of equipment that is complete andremovable for fastening to a pitch rod.

The carrier may carry a plurality of electrical energy sources that arecircumferentially equidistant around the central axis, and/or aplurality of electrical conditioning circuits that are circumferentiallyequidistant around the central axis.

In one aspect, the measurement segment may surround a hollow spaceconfigured to have said pitch rod passing therethrough without being incontact with the pitch rod, said measurement segment being arrangedlongitudinally between two rigid segments for fastening to the pitchrod.

In particular, each deformation gauge of a pitch rod may be carried by adeformable measurement segment that, surprisingly, is not itself incontact with the pitch rod.

In one possibility, the measurement segment has a cylindrical insideface of diameter that is greater than the outside diameter of an outsideface of the pitch rod, with radial clearance lying between the outsideface and the inside face.

Optionally, the two rigid segments comprise respectively theabove-mentioned first segment and second segment.

In one aspect, the detection system may comprise a plurality ofmeasurement assemblies, each measurement assembly being connected to aconcentrator by a wired or wireless connection, said concentratorcomprising at least said electrical conditioning circuit.

In one aspect, the detection system may comprise a plurality ofmeasurement assemblies arranged on respective pitch rods, together withone concentrator. The concentrator may comprise at least one energysource and/or at least one monitoring calculation means and/or at leastone antenna and/or at least one electrical conditioning circuit. Such aconcentrator serves to centralize the functions of storing electricalenergy and/or of wireless transmission and/or of processing.Furthermore, this arrangement makes it possible to lighten each piece ofequipment that is arranged on a pitch rod, thereby reducing the stressesthat result from this arrangement.

In one aspect, said at least one measurement assembly may include atleast one traction deformation gauge extending along an axial direction,the axial direction being suitable for being parallel to the extensiondirection of a pitch rod, for example.

Thus, a subassembly of a measurement assembly may comprise a tractiondeformation gauge, e.g. a strain gauge.

In one aspect, said at least one measurement assembly includes at leasttwo first bending deformation gauges arranged around a direction that,for example, is suitable for coinciding with the extension direction ofa pitch rod.

Thus, a subassembly of a measurement assembly may comprise at least twofirst bending deformation gauges, e.g. of strain gauge type, and inparticular a pair of first bending deformation gauges.

Optionally, another subassembly may comprise at least two second bendingdeformation gauges, and in particular a pair of second bendingdeformation gauges.

In an embodiment that is robust from a measurement point of view, saidat least one measurement assembly may include at least five saiddeformation gauges comprising a traction deformation gauge together withat least two first bending deformation gauges arranged around an axisand at least two second bending deformation gauges arranged around thesame axis, said two first bending deformation gauges and said two secondbending deformation gauges being offset in azimuth around the axis.

These three subassemblies serve respectively to perform respectivedifferent kinds of processing, and thus to optimize detecting wear.

The invention also provides a rotor assembly provided with a pluralityof blades and of pitch rods. Each pitch rod extends longitudinally froma first zone to a second zone, at least one of said first and secondzones comprising a ball-joint connection device. Each pitch rod may bemoved in order to modify the pitch of at least one blade, eitherdirectly or else via other mechanical members.

For example, the rotor assembly may comprise a rotary swashplatemechanically connected to each blade at least via a respective pitchrod. Optionally, the first zone of a pitch rod is provided with a firstball-joint connection device connected to the swashplate, and the secondzone is provided with a second ball-joint connection device connected toa pitch lever.

The rotor assembly includes at least one detection system of theinvention.

Each pitch lever may be hinged to a blade or to a blade cuff.

The invention also provides an aircraft provided with such a rotorassembly.

The invention also provides a detection method for detecting wear of aball-joint connection device of a pitch rod of a rotor assembly of suchan aircraft.

When at least one deformation gauge is a traction deformation gaugearranged to measure deformation along the extension direction of thepitch rod, the method may comprise the following steps:

-   -   establishing a time-varying traction measurement signal by        measuring deformation of the pitch rod with the traction        deformation gauge;    -   evaluating a current stage of flight of the aircraft; and    -   while the aircraft is flying in a level stage of flight,        detecting wear to a degree that requires replacement of the        ball-joint connection device when the time-varying traction        measurement signal presents an erroneous amplitude; and    -   while the aircraft is in an approach stage of flight,        establishing a processed measurement signal that has been        processed at least by performing a Fourier transform on the        time-varying traction measurement signal and detecting a degree        of wear that requires replacement of the ball-joint connection        device when the processed signal presents, at a predetermined        frequency or in a predetermined range of frequencies, at least        one frequency component that has an amplitude that drops below a        traction threshold during an approach.

Optionally, the time-varying measurement signal is obtained by averagingthe measurement signal over a predetermined number of revolutions of therotor assembly, in particular for a stage of level flight.

The stage of flight may be evaluated in conventional manner, e.g. byanalyzing the speed of the aircraft and/or its altitude.

The term “erroneous amplitude” refers to an amplitude that is equal toor greater than a threshold, e.g. established by testing, or else to anamplitude that is substantially different from the amplitudes observedfor the other pitch rods of a rotor assembly.

In this procedure, a traction deformation gauge can serve to emit ameasurement signal containing two indicators that are suitable for usein evaluating the presence of wear in a ball joint of a pitch rod. Afirst indicator is in the form of an erroneous amplitude for atime-varying traction signal and a second indicator is in the form ofone or more frequency components of a signal that has been processed inthe frequency domain and that is/are of amplitude less than a tractionthreshold for approach, e.g. as established by testing.

When at least one deformation gauge is a bending deformation gaugearranged to measure bending deformation, the method comprises thefollowing steps:

-   -   establishing a time-varying bending measurement signal by        measuring deformation of the pitch rod with the bending        deformation gauge; and    -   establishing a processed measurement signal that has been        processed at least by performing a Fourier transform on the        time-varying bending measurement signal, and detecting a degree        of wear that requires replacement of the ball-joint connection        device when the processed measurement signal presents, at a        predetermined frequency or in a predetermined range of        frequencies, at least one frequency component that has an        amplitude that becomes greater than a bending threshold.

Optionally, the time-varying measurement signal is obtained by averagingthe measurement signal over a predetermined number of revolutions of therotor assembly, in particular for a stage of level flight.

In this procedure, one, or indeed at least two, bending deformationgauges can enable a measurement signal to be emitted that contains anindicator that is usable and reliable for evaluating the presence ofwear in a ball joint of a pitch rod. This indicator is in the form ofone or more frequency components of a signal that has been processed inthe frequency domain and that is/are of amplitude that is greater than abending threshold, e.g. as established by testing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages appear in greater detail in the contextof the following description of embodiments given by way of illustrationand with reference to the accompanying figures, in which:

FIG. 1 is a diagrammatic view of a rotor assembly provided with adetection system of the invention;

FIG. 2 is a view of a pitch rod fitted with a detection system of theinvention;

FIG. 3 is a view of a pitch rod fitted with a carrier of the invention;

FIG. 4 is a diagram showing an example of a carrier of the invention;

FIG. 5 is a diagrammatic plan view showing a carrier of the invention;

FIG. 6 is a diagrammatic plan view showing a carrier of the invention;

FIG. 7 is a fragmentary view of a rotary assembly provided withdetection system carriers;

FIG. 8 is a graph showing a time-varying measurement signal emittedduring a stage of level flight from a traction deformation gaugearranged on a pitch rod that presents a ball-joint connection devicewith no wear;

FIG. 9 is a graph showing a time-varying measurement signal emittedduring a stage of level flight from a traction deformation gaugearranged on a pitch rod that presents a ball-joint connection devicewith medium wear;

FIG. 10 is a graph showing a time-varying measurement signal emittedduring a stage of level flight from a traction deformation gaugearranged on a pitch rod that presents a ball-joint connection devicethat is very worn and that is to be removed;

FIG. 11 is a graph showing a time-varying measurement signal emittedduring an approach stage from a traction deformation gauge arranged on apitch rod that presents a ball-joint connection device with no wear;

FIG. 12 is a graph showing a time-varying measurement signal emittedduring an approach stage from a traction deformation gauge arranged on apitch rod that presents a ball-joint connection device with medium wear;

FIG. 13 is a graph showing a time-varying measurement signal emittedfrom a traction deformation gauge arranged on a pitch rod that presentsa ball-joint connection device that is very worn and that is to beremoved;

FIG. 14 is a graph showing a processed measurement signal obtained froma signal emitted during an approach stage from a traction deformationgauge arranged on a pitch rod that presents a ball-joint connectiondevice with no wear;

FIG. 15 is a graph showing a processed measurement signal obtained froma signal emitted during an approach stage from a traction deformationgauge arranged on a pitch rod that presents a ball-joint connectiondevice that is worn and that is to be removed; and

FIG. 16 is a graph showing both a processed measurement signal obtainedfrom a measurement signal emitted from a bending deformation gaugearranged on a pitch rod presenting a healthy ball joint and also aprocessed measurement signal obtained from a measurement signal emittedfrom a bending deformation gauge arranged on a pitch rod presenting aball-joint connection device that is worn and that is to be removed.

DETAILED DESCRIPTION

FIG. 1 shows an embodiment of a detection system 30 of the inventionseeking to detect wear of a ball-joint connection device, referred tomore simply as a “ball joint”.

By way of example, such a detection system 30 may be arranged on a rotorassembly 5, and in particular on a rotor assembly 5 of an aircraft 1, inorder to detect wear of a ball-joint connection device 25 of a pitch rod20.

Specifically, such a rotor assembly 5 may include a plurality of blades10. Each blade 10 is carried by a rotor head not shown, possibly via acuff 11 and/or via hinge and retaining devices. Certain blades mayinclude cuffs that are integrated therein.

The rotor assembly 5 also includes multiple pitch rods, and in FIG. 1 itincludes one pitch rod 20 for each blade 10 in order to connect eachblade 10 to flight controls. Each pitch rod 20 extends longitudinallyalong its extension direction D1 from a first zone 21 to a second zone22, the first zone 21 and/or the second zone 22 including a ball-jointconnection device 25. For example, the first zone 21 is hinged to arotary swashplate 8 of a set of swashplates 6, optionally via a firstball-joint connection device 26, and the second zone 22 is hinged to apitch lever 9, optionally via a second ball-joint connection device 27.The non-rotary swashplate 7 is then controlled by flight controls, e.g.via servocontrols or via other pitch rods.

The rotor assembly 5 then has at least one detection system 30 of theinvention for detecting wear of at least one ball-joint connectiondevice 25 of at least one pitch rod 20.

FIGS. 1 to 7 show various non-restrictive embodiments of a detectionsystem 30 of the invention, and FIGS. 8 to 16 comprise graphs showing amethod of detecting wear of a ball-joint connection device 25 by meansof such a detection system.

Independently of the embodiment, a detection system 30 includes at leastone measurement assembly 31, and for example it may include onemeasurement assembly 31 for each blade. Such a measurement assembly 31is provided with at least one measurement subassembly including at leastone deformation gauge for placing on a pitch rod 20 that is to bemonitored.

A measurement assembly 31 may include a traction-measurement subassembly32. The traction-measurement subassembly 32 comprises at least onetraction deformation gauge 33. The traction deformation gauge 33 mayextend along an axial direction, optionally suitable for being parallelto the extension direction D1 of a pitch rod 20 so as to deform when thepitch rod 20 is stretched or compressed. For example, where appropriate,such an extension direction D1 passes through the centers both of afirst ball-joint connection device 26 and also of a second ball-jointconnection device 27 of the pitch rod 28.

A measurement assembly 31 may include at least one first bendingmeasurement subassembly 34. For example, the first bending measurementsubassembly 34 may include at least two first bending deformation gauges35 and 36 arranged around a direction optionally suitable for coincidingwith the extension direction D1.

A measurement assembly 31 may include at least one second bendingmeasurement subassembly 37. For example, the second bending measurementsubassembly 37 may include at least two second bending deformationgauges 38 and 39 that are arranged around the extension direction D1 andthat are offset in azimuth relative to the first deformation gauges 35and 36.

In the example shown, a measurement assembly 31 may thus comprise inparticular one traction deformation gauge 33 together with two firstbending deformation gauges 35 and 36, and two second bending deformationgauges 38 and 39.

In another aspect, the detection system 30 comprises at least oneelectrical conditioning circuit 40 connected to at least one deformationgauge 33, 35, 36, 38, 39, and for example comprises one electricalconditioning circuit 40 for each measurement subassembly 32, 34, 37. Theelectrical conditioning circuit(s) 40 may be carried by a pitch rod 20or may be arranged within a concentrator 90 arranged on the rotor head.

Furthermore, a detection system 30 includes at least one electricalenergy source 50, and for example may include an electrical energysource 15 for each measurement subassembly 32, 34, 37. The electricalenergy source(s) 50 may be carried by a pitch rod 20 or may be arrangedwithin a concentrator 90.

Under such circumstances, each electrical conditioning circuit 40receives electrical energy in order to prepare a measurement signal thatvaries as a function of the deformation of a deformation gauge 33, 35,36, 38, 39 and as a function of said wear. For example, an electricalconditioning circuit 40 may comprise a Wheatstone bridge circuitincluding each deformation gauge 33, 35, 36, 38, 39 of a measurementsubassembly. Furthermore, the electrical conditioning circuit 40 mayinclude a voltmeter or the equivalent that emits a time-varyingmeasurement signal relating to a potential difference that varies overtime as a function of the deformation of the deformation gauges, whichdeformation varies as a function of the wear of a ball-joint connectiondevice 25. Also, and by way of example, an electrical conditioningcircuit 40 may include a memory for storing the emitted measurementsignal.

Furthermore, a detection system 30 may include monitoring calculationmeans 60 that are connected by a wired or wireless connection to atleast one electrical conditioning circuit 40. For example, a detectionsystem 30 may comprise monitoring calculation means 60 connected to asingle electrical conditioning circuit 40 and optionally carried by apitch rod 20, or it may comprise respective monitoring calculation means60 connected to each of the electrical conditioning circuits 40 of apitch rod 20 and optionally carried by that pitch rod, or indeed it maycomprise monitoring calculation means 60 arranged in a concentrator 90and connected to at least one electrical conditioning circuit 40.Optionally shared calculation means 60 may also be arranged away fromthe rotor assembly 5.

By way of example, each monitoring calculation means 60 may comprise atleast one processor or the equivalent, at least one memory, at least oneintegrated circuit, at least one programmable system, and/or at leastone logic circuit, these examples not limiting the scope to be given tothe term “monitoring calculation means”.

Each monitoring calculation means 60 is configured to process at leastone measurement signal emitted by an electrical conditioning circuit 40in order to determine the presence of wear to a degree that requiresmaintenance action on the pitch rod 20 if the measurement signalprocessed by the monitoring calculation means 60 presents apredetermined anomaly.

Optionally, a detection system 30 may include warning means 70 in wiredor wireless connection with at least one monitoring calculation means60. The monitoring calculation means 60 transmit a signal to the warningmeans 70 that generate, where appropriate, a warning when a processedmeasurement signal presents a predetermined anomaly.

Furthermore, the detection system 30 may include one or more antennasfor providing wireless connections.

For example, at least one first antenna 75 is used for transmitting asignal away from the rotor assembly 5. Thus, a first antenna 75 may beconnected to an electrical conditioning circuit 40 in order to transmita measurement signal to monitoring calculation means 60 present awayfrom the rotor assembly 50. In another example, at least one firstantenna 75 may be connected to monitoring calculation means 60 in orderto transmit a signal, e.g. to warning means 70. The monitoringcalculation means 60 may communicate with other monitoring calculationmeans 60, likewise via antennas.

FIG. 2 shows an embodiment. In this embodiment, the measurement assembly31 is carried directly by the pitch rod 20, e.g. being fastened theretoby attachment means. By way of example, each deformation gauge 33, 35,36, 38, 39 is adhesively bonded on the pitch rod 20 between the firstzone 21 and the second zone 22 of the pitch rod.

In this embodiment, each measurement subassembly 32, 34, 37 is connectedby a wired connection to a respective electrical conditioning circuit40. By way of example, the electrical conditioning circuit 40 islikewise adhesively bonded on the pitch rod 20. Alternatively, it may bearranged in a concentrator that is constrained to rotate with the rotorassembly 5.

In this embodiment, each electrical conditioning circuit 40 is connectedto one or more sources of electrical energy, optionally adhesivelybonded on the pitch rod 20 or else arranged in a concentrator 90 that isconstrained to rotate with the rotor assembly 5.

FIG. 3 shows another embodiment.

In this embodiment, a detector system 30 includes at least one carrier80, and by way of example one carrier 80 for each pitch rod. The carrier80 is hollow in its center so as to surround a segment of the pitch rod20. The carrier 80 may be threaded onto the pitch rod 20 or it maycomprise elements for fastening together, e.g. such as two half-shellsfor screwing together.

The carrier 80 may be provided with a fastener device 85 to enable it tobe fastened to the pitch rod 20 that is to be monitored. Such a fastenerdevice 85 may include high and low abutments for switching between twonuts 23 and 24 of the pitch rod, nut-and-bolt systems, . . . .

Furthermore, the carrier 80 possesses a measurement segment 81 that iselastically deformable, optionally for amplifying deformation of thepitch rod. For example, the measurement segment 81 may comprise anelastomer ring. The measurement segment 81 carries a measurementassembly 31, with each deformation gauge of the measurement assembly 31being adjacent to the measurement segment or else embedded in themeasurement segment 81, for example.

With reference to FIG. 4, the measurement segment 81 need not be incontact with the pitch rod 20, at least when at rest, i.e. when there isno deformation of the pitch rod. By way of example, the measurementsegment 81 surrounds a hollow space 84 through which the pitch rod 28passes, and without coming into contact with the pitch rod 20. In theembodiment shown, the measurement segment 81 presents an inside diameter100 that is greater than the outside diameter of a segment of the pitchrod 20 that is surrounded by the measurement segment 81.

Optionally, the measurement segment 81 is arranged longitudinally, i.e.along the longitudinal extension direction D1 of the pitch rod 20between two rigid segments 82 and 83 that are for fastening to the pitchrod 20.

For example, the carrier 80 may have a segment fitted with at least oneelectrical energy source 50 in order to have its own energy supply,and/or at least one electrical conditioning circuit 40, and/or at leastone monitoring calculation means 60, and/or at least one antenna 75. Inan example, such a segment may be the measurement segment.

In the embodiment shown, a first segment 82 carries a respectiveelectrical energy source 50 for each measurement subassembly.Furthermore, a second segment 83 carries at least one electricalconditioning circuit 40, and/or at least one monitoring calculationmeans 60, and/or at least one antenna 75, the measurement segment 81being arranged between the first segment 82 and the second segment 83.

In this embodiment, the carrier 80 includes in particular oneelectronics card 41 for each measurement subassembly, i.e. threeelectronics cards 41 respectively for a single traction measurementsubassembly 32, for the first bending measurement subassembly 34, andfor the second bending measurement subassembly 37.

Under such circumstances, each electronics card 41 comprises anelectrical conditioning circuit 40 connected by a wired connection toeach deformation gauge of the associated measurement subassembly, andalso to an energy source 50. Furthermore, the electronics card 41 maycarry respective monitoring calculation means 60 connected to theelectrical conditioning circuit 40 by a wired connection.

Also, the monitoring calculation means 60 may be connected to a commonfirst antenna 75 and/or to respective antennas.

With reference to FIGS. 5 and 6, the electrical energy sources 50 andthe electronics cards may be positioned so as to balance the carrier 80in order to ensure that the carrier 80 does not interfere with thedesign of the pitch rod 20.

FIG. 7 shows a rotor assembly 5 including pitch rods 20 provided withcarriers 80. Optionally, the carriers 80 need not include monitoringcalculation means, the various electrical conditioning circuits 40 beingconnected by wired or wireless connections to at least one monitoringcalculation means of a concentrator 90. Optionally, the carriers 80 neednot include electrical energy sources, the various electricalconditioning circuits 40 being connected by wired connections toelectrical energy sources 50 of a concentrator 90.

FIGS. 8 to 16 comprise various graphs for showing methods implemented bya detection system of the invention.

In particular, FIGS. 8 to 10 show wear of a ball-joint connection device25 being detected by means of a time-varying measurement signal emittedby an electrical conditioning circuit 40 from a traction deformationgauge 33.

In this method, the electrical conditioning circuit normally emits anelectrical signal in the form of a time-varying signal measuringtraction that varies over time as a function of the deformation intraction and/or compression of the traction deformation gauge 33.

This time-varying measurement signal may optionally be processed byconventional sampling methods or by averaging over a predeterminednumber of revolutions of the rotor assembly 5.

Furthermore, the current stage of flight of the aircraft 1 is determinedby conventional instruments.

The current stage of flight and the time-varying measurement signal mayoptionally be stored in a memory or they may be processed by monitoringcalculation means 60.

FIG. 8 shows the time-varying measurement signal obtained for onerevolution during a stage of level flight with a pitch rod that ishealthy. FIG. 9 shows the time-varying measurement signal obtained overone revolution during a stage of level flight with a pitch rod thatpresents a ball-joint connection device with a degree of wear that isacceptable. FIG. 10 shows the time-varying measurement signal obtainedover one revolution during a stage of level flight with a pitch rod thatpresents a ball-joint connection device with a degree of wear thatrequires maintenance action. FIGS. 8 to 10 thus comprise graphs, eachplotting time along an abscissa axis and a potential difference up anordinate axis, each curve showing a measurement signal that presents apotential difference that varies as a function of time.

An operator can perceive a defect visually by observing the maximumamplitude 110 of the time-varying measurement signal. The greater theamount of wear of a ball-joint connection device, the higher thismaximum amplitude 110. It is thus possible to establish a threshold thatis the image of a degree of wear requiring maintenance action.

Thus, while the aircraft 1 is in a stage of level flight, the method maycomprise a step of detecting wear requires the ball-joint connectiondevice 25 to be replaced once the time-varying traction measurementsignal presents an erroneous amplitude, e.g. an amplitude greater thanor equal to a threshold or that is different from the amplitudes ofmeasurement signals coming from other pitch rods. This analysis may beperformed visually by an operator or automatically by the monitoringcalculation means.

FIG. 11 shows the time-varying measurement signal obtained over onerevolution during an approach stage from a traction deformation gauge ona pitch rod that is healthy. FIG. 12 shows the time-varying measurementsignal obtained over one revolution during an approach stage from atraction deformation gauge on a pitch rod presenting a ball-jointconnection device having a degree of wear that is acceptable. FIG. 13shows the time-varying measurement signal obtained over one revolutionduring an approach stage from a traction deformation gauge on a pitchrod presenting a ball-joint connection device having a degree of wearthat requires a maintenance action.

An operator can perceive a defect visually by observing the appearanceof the time-varying measurement signal. The greater the amount of wearof a ball-joint connection device, the greater the extent to which thesignal is “smoothed”, as can be seen by looking at the segments 120 ofthe signals visible in FIGS. 11 to 13. Specifically, any clearance thatis present in a ball-joint connection device has the effect of filteringout some fraction of the vibration in a pitch rod as induced by theresonant modes of vibration in the blade connected to the pitch rod andin lower dynamic assemblies.

In order to perform automatic processing, while the aircraft 1 is in anapproach stage, the monitoring calculation means can process thetime-varying traction measurement signal at least by performing aFourier transform in order to obtain a processed measurement signal.

FIGS. 14 and 15 show such a processed measurement signal. FIG. 15 thuspresents a graph having frequencies plotted along the abscissa axis andenergy plotted up the ordinate axis. Frequency components of theprocessed measurement signal present attitudes the decrease in FIG. 15when at least one ball-joint connection device presents wear thatrequires maintenance action.

Under such circumstances, the monitoring calculation means can detectwear that requires the ball-joint connection device 25 to be replacedwhen the processed signal presents, at a predetermined frequency or in apredetermined range of frequencies, one or more frequency components ofamplitude dropping below a traction threshold during an approach orduring level flight.

When at least one deformation gauge is a bending deformation gauge 35,36, 38, 39, the electrical conditioning circuit emits in normal manneran electrical signal in the form of a time-varying bending measurementsignal that varies as a function of the deformation of the deformationgauge.

This time-varying measurement signal may optionally be processed byconventional sampling methods or by averaging over a predeterminednumber of revolutions of the rotor assembly 5.

The time-varying measurement signal may optionally be stored in amemory.

Thereafter, monitoring calculation means can process the time-varyingbending measurement signal at least by performing a Fourier transform inorder to obtain a processed bending measurement signal.

FIG. 16 plots a first curve C1 that shows such a processed bendingmeasurement signal emitted from a pitch rod that is healthy and a secondcurve C2 that shows such a processed bending measurement signal emittedfrom a pitch rod having a ball-joint connection device that is worn. Inthe presence of wear, numerous frequency components present increasedamplitude.

Under such circumstances, the monitoring calculation means can detectwear that requires the ball-joint connection device 25 to be replacedwhen the processed signal presents, at a predetermined frequency or in apredetermined range of frequencies, one or more frequency components ofamplitude rising above a bending threshold.

Naturally, the present invention may be subjected to numerous variationsas to its implementation. Although several embodiments are described, itshould readily be understood that it is not conceivable to identifyexhaustively all possible embodiments. It is naturally possible toenvisage replacing any of the means described by equivalent meanswithout going beyond the ambit of the present invention.

The invention claimed is:
 1. A detection system for detecting wear of aball joint connection device of a pitch rod of a rotor assembly; whereinthe detection system includes at least one measurement assembly, the atleast one measurement assembly having at least one deformation gauge forplacing on the pitch rod, the detection system comprising at least oneelectrical conditioning circuit connected to at least one of the atleast one deformation gauge and to at least one electrical energysource, the electrical conditioning circuit being configured to generatea measurement signal that varies as a function of deformation of the atleast one deformation gauge and as a function of the wear, the detectionsystem including a carrier, the carrier being provided with a fastenerdevice for fastening to the pitch rod that is to be monitored, thecarrier including an elastically deformable measurement segment carryingthe measurement assembly, the measurement segment surrounding a hollowspace configured to have the pitch rod passing therethrough withoutbeing in contact with the pitch rod, the measurement segment beingarranged longitudinally between two rigid segments for fastening to thepitch rod.
 2. A detection system according to claim 1; wherein thedetection system comprises monitoring calculation means in communicationwith the at least one electrical conditioning circuit, the monitoringcalculation means being configured to process the measurement signal andto determine whether the wear is present to a degree that requiresmaintenance action on the pitch rod when the measurement signal asprocessed by the monitoring calculation means presents a predeterminedanomaly.
 3. A detection system according to claim 2; wherein thedetection system includes warning means in communication with themonitoring calculation means, the monitoring calculation means beingconfigured to control the warning means in order to signal the presenceof wear when the measurement signal as processed presents thepredetermined anomaly.
 4. A detection system according to claim 1;wherein the detection system includes at least a first antenna fortransmitting away from the rotor assembly either the measurement signalor else a signal emitted by a monitoring calculation means connected tothe electrical conditioning circuit, the first antenna being connectedto the electrical conditioning circuit or to the monitoring calculationmeans.
 5. A detection system according to claim 1; wherein the twosegments comprise a first segment including the at least one electricalenergy source and a second segment including the at least one electricalconditioning circuit.
 6. A detection system according to claim 1;wherein the measurement segment includes at least one energy source orof an electrical conditioning circuit.
 7. A detection system accordingto claim 1; wherein the detection system comprises a plurality ofmeasurement assemblies, each measurement assembly being connected to aconcentrator by a wired or wireless connection, the concentratorcomprising at least the electrical conditioning circuit.
 8. A detectionsystem according to claim 1; wherein the at least one measurementassembly include at least one traction deformation gauge extending alongan axial direction suitable for being parallel to the extensiondirection (D1) of a pitch rod.
 9. A detection system according to claim1; wherein the at least one measurement assembly include at least twofirst bending deformation gauges arranged around a direction suitablefor coinciding with the extension direction (D1) of a pitch rod.
 10. Adetection system according to claim 1; wherein the at least onemeasurement assembly include at least five deformation gauges comprisinga traction deformation gauge together with at least two first bendingdeformation gauges arranged around an axis and at least two secondbending deformation gauges arranged around the axis, the two firstbending deformation gauges and the two second bending deformation gaugesbeing offset in azimuth around the axis.
 11. A rotor assembly providedwith a plurality of blades and of pitch rods, each pitch rod extendinglongitudinally from a first zone to a second zone, at least one of thefirst and second zones including a ball joint connection device; whereinthe rotor assembly includes at least one detection system according toclaim 1, with each pitch rod carrying a measurement assembly.
 12. Anaircraft including a rotor assembly according to claim
 11. 13. Adetection system according to claim 1; wherein the elasticallydeformable measurement segment has an inside diameter that surrounds asegment of the pitch rod, the inside diameter of the elasticallydeformable measurement segment is greater than an outside diameter ofthe pitch rod.
 14. A detection system according to claim 1; wherein theelastically deformable measurement segment comprises an elastomericring.
 15. A detection system according to claim 14; wherein theelastomeric ring has an inside diameter that surrounds a segment of thepitch rod, the inside diameter of the elastomeric ring is greater thanan outside diameter of the pitch rod.
 16. A detection system accordingto claim 1; wherein the fastener device is fastened to the pitch rodthat is to be monitored and the two rigid segments are fastened to thepitch rod.
 17. A detection system according to claim 16; wherein thepitch rod is connected to a ball-joint.
 18. A detection method fordetecting wear of a ball-joint connection device of a pitch rod of arotor assembly of the aircraft, the rotor assembly being provided with aplurality of blades and of pitch rods, each pitch rod extendinglongitudinally from a first zone to a second zone, at least one of thefirst and second zones comprising a ball-joint connection device, therotor assembly including at least one detection system including atleast one measurement assembly having at least one deformation gauge forplacing on the pitch rod, the detection system including at least oneelectrical conditioning circuit connected to at least one of the atleast one deformation gauge and to at least one electrical energysource, the electrical conditioning circuit being configured to generatea measurement signal that varies as a function of deformation of the atleast one deformation gauge and as a function of the wear; wherein atleast one deformation gauge is a traction deformation gauge arranged tomeasure deformation along the extension direction of the pitch rod andthe method comprises the following steps: establishing a time-varyingtraction measurement signal by measuring deformation of the pitch rodwith the traction deformation gauge; evaluating a current stage offlight of the aircraft; and while the aircraft is flying in a levelstage of flight, detecting wear to a degree that requires replacement ofthe ball-joint connection device when the time-varying tractionmeasurement signal presents an erroneous amplitude, and/or while theaircraft is in an approach stage of flight, establishing a processedmeasurement signal at least by performing a Fourier transform on thetime-varying traction measurement signal and detecting a degree of wearthat requires replacement of the ball-joint connection device when theprocessed measurement signal presents, at a predetermined frequency orin a predetermined range of frequencies, at least one frequencycomponent that has an amplitude that drops below a traction thresholdduring an approach.
 19. A detection method for detecting wear of aball-joint connection device of a pitch rod of a rotor assembly of theaircraft, the rotor assembly being provided with a plurality of bladesand of pitch rods, each pitch rod extending longitudinally from a firstzone to a second zone, at least one of the first and second zonescomprising a ball-joint connection device, the rotor assembly includingat least one detection system including at least one measurementassembly having at least one deformation gauge for placing on the pitchrod, the detection system including at least one electrical conditioningcircuit connected to at least one of the at least one deformation gaugeand to at least one electrical energy source, the electricalconditioning circuit being configured to generate a measurement signalthat varies as a function of deformation of the deformation gauge(s) andas a function of the wear; wherein at least one deformation gauge is abending deformation gauge arranged to measure bending deformation of thepitch rod, and the method comprises the following steps: establishing atime-varying bending measurement signal by measuring deformation of thepitch rod with the bending deformation gauge; and establishing aprocessed measurement signal at least by performing a Fourier transformon the time-varying bending measurement signal, and detecting a degreeof wear that requires replacement of the ball-joint connection devicewhen the processed measurement signal presents, at a predeterminedfrequency or in a predetermined range of frequencies, at least onefrequency component that has an amplitude that becomes greater than abending threshold.